The Symphonie has approximately 1.5 days of internal memory. Whenever a new MMC is inserted in the logger, the most recent 1.5 days of data will be written to the MMC.
The internal memory is designed to maintain data continuity and seamless data collection when changing memory cards and should not be relied upon to store beyond a day and a half of data.

Q: Does NRG plan to develop any tools that will aid in identifying and cleaning these areas of bad data?
A: We are working closely with our round table experts and hope to share some of our findings on techniques and methodologies to address this issue.

Q: What is the expected timing for recommendations/conclusions on how to fully identify/correct problems with sensor drag?
A: Some experts in the industry are developing their own methodologies for data analysis. Our expectation is that these results will be presented at future conferences.

Q: What is the magnitude of additional uncertainty that a dragging sensor is estimated to cause (%)?
A: The magnitude of uncertainty will vary based on the tower configuration and data analysis methodology. We understand that the error can be 1%, but additional data quality checks can reduce this to less than 1%.

Q: Is there a standard uncertainty value that will be added and has this been quantified by GH, AWS, or DNV-GEC?
A: We have engaged a group of industry experts to provide us with input and feedback while we resolve this issue. Each data analysis expert has his own methods and techniques for analyzing data and mitigating uncertainty.

Q: Could you elaborate on recommendations for how to use data from masts with corrupted sensors?
A: It is best to compare the ten-minute average of two sensors that are mounted at the same height. By looking at the difference (or ratio) between these two sensors, it can be determined whether one or both are experiencing excessive drag. (See slides 8 and 10 in the presentation for a visual depiction.) Typical data quality checks can then be used to filter the data. If unsure, it is best to consult an expert in data analysis.

Q: What are the criteria for replacing an instrument? Will NRG liberally replace any sensor showing signs of this problem in 10-minute data, even if your post-calibration tests do not excite the vibration mode in the sensor?
A: If you have a sensor that is showing signs of this problem, NRG Systems will replace it under warranty based on the data analysis report alone. To clarify, the calibration process itself does not excite the sensor into a vibratory mode.

Q: What is your recommendation on parallel installs other manufacturers' sensors alongside the 40C to compare the data (i.e. at what height and direction to install new, third party sensors)?
A: There is no consensus on best practice as it relates to tower configuration; preferences will vary depending on priorities. Some of our customers pair different anemometers with #40Cs at the same level. The height and direction is typically dictated by site conditions and prevailing winds.

Q: Do you have an estimated timeline for when field testing and reengineering [sic] will be complete?
A: We can?t provide specific timelines. Our validation criteria require that we collect data from 50 pairs of anemometers for eight weeks. Only when we have sufficient data, and consensus that the sensors are performing up to pre-2006 standards, will we form conclusions and move ahead. There is a short amount of time on either side of those eight weeks to complete engineering activities, deploy sensors, and ramp up manufacturing.

Q: Has this problem been seen on both tubular and lattice towers? Also, has this problem been seen on varying boom lengths/types?
A: We have seen sensor dragging on both tubular and lattice towers, and on booms of various geometries and manufacturers.

Q: Can NRG specify by serial number which sensors can enter the vibratory mode? How do we determine if sensors delivered are within the problem batch(es)?
A: #40C anemometers with serial numbers 26130 - 92049 are potentially affected. This is not a batch issue. It is a function of the individual sensor and its susceptibility to entering a vibratory mode.

Q: What percentage of returned anemometers has this issue?
A: Some customers report no incidences and some customers report higher frequencies of affected anemometers. Based on all of the data and sensors we?ve examined, we estimate that 20%-30% of sensors manufactured after 2006 are affected.

Q: How do we determine if the data we have collected is valid?
A: Comparing two sensors mounted at the same level by taking the difference (or ratio) of the ten-minute average readings is the simplest method. The two sensor readings should track fairly well, but if one sensor is in this vibratory mode, then the difference (or ratio) between the two will diverge. Keep in mind that two sensors at the same level may not track exactly the same due to other factors (e.g. wind regime, mounting configuration, site terrain, etc). The level of scatter should be excessive. If unsure, it is always best to consult a data analysis expert.

Q: Is it possible to send anemometers back to identify if they are vulnerable to vibration?
A: Vulnerability is difficult to assess due to the randomness of this phenomenon. It is better to continue to analyze your data and use it to mitigate uncertainty if excessive scatter is present. It is also possible to perform post-calibration on an anemometer to determine its condition.

Q: Once an anemometer shows signs of dragging, how often will it go into the vibratory mode? 30% of the time in 5-10m/s wind? 70%?
A: An anemometer susceptible to the vibratory mode will tend to switch into its normal mode at higher wind speeds (above 10 m/s) and at very low wind speeds (below 5 m/s). In the 5-10 m/s range it will vary by sensor and its environment. In answer to this specific question, we don't have a basis by which to identify a typical percentage. We estimate that 20-30% of all sensors manufactured after 2006 are affected by this issue.